1. Field of the Invention
The present invention relates to a variable compression ratio engine. More particularly, the present invention relates to a variable compression ratio engine, which may absorb combustion impact and may improve durability.
2. Description of Related Art
In general, the compression ratio of an internal combustion engine is represented by the largest volume of a combustion chamber prior to compression and the smallest volume of the combustion chamber after compression in a compression stroke of the internal combustion engine.
The output of the internal combustion engine increases as the compression ratio of the internal combustion engine is increased. However, if the compression ratio of the internal combustion engine is too high, so-called knocking occurs, and this even decreases the output of the internal combustion engine and also results in overheating of the internal combustion engine, a failure in a valve or piston of the internal combustion engine, and so on.
Accordingly, the compression ratio of the internal combustion engine is set to a specific value within an appropriate range prior to the occurrence of knocking. As such, because the air-fuel ratio and output of the internal combustion engine can be improved by properly varying the compression ratio according to the load of the internal combustion engine, various approaches are being proposed to vary the compression ratio of the internal combustion engine.
These approaches for varying the compression ratio of the internal combustion engine mostly employ methods that vary the volume of the compression chamber during a compression stroke.
For example, there have been proposed methods that vary the height of the top dead center of a piston during a compression stroke, or increase or decrease the volume of a sub-compression chamber provided in a cylinder head.
Varying the height of the top dead center of a piston tends to make the structure of the internal combustion engine complicated. Therefore, it will be desirable to vary the compression ratio by providing a sub-compression chamber in a cylinder head to make the structure simple and achieve great improvement in air-fuel ratio.
However, since combustion impact in a combustion stroke is directly transmitted to elements of a variable compression ratio device so that durability of the elements may be deteriorated.
The above information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.